As lithium ion secondary batteries which are excellent in an energy density and are spread for a portable apparatus, batteries, in which a laminated film is used for an exterior packaging member, have been put into practical use because the energy density of the batteries is high at a light weight, and the batteries can be manufactured in a very thin shape.
In addition, in the batteries in which the laminated film is used as the exterior packaging member as described above, an electrolytic solution and a polymer compound are used as an electrolyte so as to obtain liquid leakage resistance and the like, and the batteries are known as polymer batteries. Among these batteries, a battery that uses a gel electrolyte, in which an electrolytic solution is retained by a polymer compound and has a so-called gel shape, is widely spread.
In a polymer battery, since an aluminum laminated film is used as the exterior packaging member, the degree of freedom in shape is greatly improved. However, strength is not sufficient in some cases. Therefore, when a strong force is applied thereto due to improper use, deformation is likely to occur.
In this case, when the polymer battery is covered with a strong exterior pack, there is no problem. However, the exterior pack becomes simple in accordance with a demand for a recent high capacity. Therefore, when the deformation is great, short-circuit is likely to occur at the inside of the battery, and there is a possibility that the battery does not function as a battery.
In contrast, Patent Document 1 suggests that particles of alumina and the like are mixed in a gel electrolyte to improve the strength of the gel.